It is known that a white LED emitting light which looks white is composed of a light emitting diode emitting blue light and phosphor excited by this blue light to emit yellow light (including yellow green color and orange color). Since the wavelength range of blue light emitted from a light emitting diode is from 350 to 500 nm, phosphor excited by light having this wavelength range and emitting yellow fluorescence is used as phosphor for white LED. Therefore, desirable phosphor is phosphor that has a peak wavelength of excited spectrum within the wavelength range of from 350 to 500 nm, excites efficiently by light in this wavelength range and emits yellow fluorescence.
As the phosphor used for a white LED composed of a light emitting diode emitting blue light and fluorescence excited by this blue light to emit yellow fluorescence and showing a peak wavelength of excitation spectrum within the wavelength range of from 350 to 500 nm, Japanese Patent Application No. 2001-214162A, for example, suggests an oxynitride glass phosphor activated by europium (composition molar ratio: CaO:Al2O3:SiO2:AlN:Eu2O3=29.1:3.2:32.3:32.3:3.1). This fluorescence shows a peak wavelength of excitation spectrum of 480 nm, within the wavelength range of from 350 to 500 nm, however, its peak wavelength of luminescence spectrum is 600 nm and it emits near red fluorescence. Therefore, when this phosphor is used for a white LED, the white LED emit slightly different form white light and this fluorescence is insufficient as the fluorescence for white LED.
As the other example of the phosphor used for a white LED, the compound represented by (Y1−aGda)3(Al1−bGab)5O12:Ce is practically used (Japanese Patent Application No. H10-242513A). Since the peak wavelength of luminescence spectrum contains the blue-green fluorescence having the wavelength of 480 nm with about 20% intensity of the emission, when this phosphor is combined with blue LED, this phosphor emit greenish yellow fluorescence and is insufficient as white LED.